OP ARTS AND SCIENCES. 17 



10 Mo0 3 • Na 2° • 3 H 2° + 9 a( i or M o 10 O2 6 ( NaO )2( H O)6 4- 9 aq 



14 Mo0 8 . 6 Na 2 -f- 44 aq " Mo 14 3B (NaO) 12 + 44 aq 



16 M0O3 . 2 Na 2 . 5 H 2 + 3 aq " Mo 16 O 41 (NaO) 4 (HO) 10 -f 3 aq 



18 M0O3 . 2 BaO . 6 H 2 6 -f 2 aq " Mo 18 4G (Ba0 2 ) 2 (HO) 12 -j- 2 aq 



It may of course be maintained that the arrangement of the acid 

 salts of molybdic oxide which I have adopted is purely arbitrary, and 

 that they might be written with equal or greater probability in the 

 usual manner, as members of the normal series, which would then be : 



Mo0 3 . Na 2 + 2 aq 8 Mo0 3 . Na 2 + 2 aq 



2 M0O3 . Na 2 -f aq 9 Mo0 3 . BaO -j- 4 aq 



3 M0O3 • Na 2° + 7 aq 10 M0O3 . Na 2 -j- 12 aq 



4 Mo0 8 . Na 2 -j- 6 aq 16 Mo0 3 . Na 2 + 9 aq. 



To this I reply that one arrangement is no more arbitrary than the 

 other, since we have no positive knowledge of the constitution of 

 these salts, their molecular weights being, as in the case of most inor- 

 ganic compounds, entirely unknown. The commonly received view 

 is therefore also a pure assumption. In any case, however, we have 

 the two salts, represented respectively by the formulas 



4 Mo0 3 . Na 2 -f 6 aq or Mo 4 O n (NaO) 2 -f 6 aq 



1 4 Mo0 8 . 6 Na 2 -4- 44 aq " Mo 14 36 (NaO )~ 2 + 44 aq, 



forming the upper and lower limits of a molybdic series corresponding 

 to alkaline tungstates, and from these we may fairly infer the exist- 

 ence of the intermediate compounds. But one acid tungstate of the 

 meta series is at present known, the salt 



8 W0 3 . Na 2 '4- 12 aq, or W 8 23 (NaO) 2 -f 12 aq. 



This may be considered as an acid salt of the 8-atom term, and written 



8 W0 3 . Na 2 . 2 H 2 + 10 aq, 



so that it will correspond to the molybdic salt 



8 Mo0 3 . Na 2 . 2 H.,0 + 2 aq. 



But the supposition that acid metatungstates of the 4 : 1 series really 

 exist, is in no way inconsistent with the view of the whole subject 

 which I have taken. So far as I know, no attempt has been made to 

 exhibit the mode of union of the elements in the higher tungstates. 

 Our views of the subject will differ according as we consider tungsten 



vol. xv. (n. s. vii.) 2 



